Power transistors such as five-leaded TO-220 packages are commonly used in many electronic devices and modules. During operation, the TO-220 packages generate a great deal of heat which is normally dissipated through a metal header built into the TO-220 package. However, radiant heat transfer alone may not be sufficient to avoid damage to the electronic internals of the power transistor. In such cases, it is desirable to conduct heat away from the transistor and to a heat sink. However, the metal header built into the TO-220 package is at an operating voltage, so the header must be insulated before coming into contact with a grounded metallic heat sink.
One method of insulating the TO-220 headers is to apply a silicon-based tape which acts as both an electrical insulator and a facilitator of heat transfer. Prior to delivery to a lead cutting and forming machine, such as that disclosed in U.S. Pat. No. 4,757,600 to Holcomb, the TO-220 packages are, therefore, typically adhered to one side of the tape. The tape is then wound onto a reel, which can be unwound to supply parts to the cutting and forming machine.
The transistor packages can be joined to the tape either manually or automatically. However, neither method of depositing the packages on the insulating tape reliably maintains a regular spacing, or pitch, between adjacent packages. Furthermore, the tape which holds the components is not usually separated into individual segments by the machine until after the lead cutting and forming operations have been performed. Because the lead cutting and forming operations are performed at regular intervals, these machines require the parts on the tape to be at a well known distance from each other. Such machines are, therefore, dependent on the pitch between adjacent parts. If the variance of the part pitch is outside narrow tolerances, the die presses which normally perform the cutting and forming operations do not strike the components correctly. The die presses may then become jammed or misaligned, and the resulting misformed parts must be scrapped.